Center for Asthma & Environmental Exposure

Asthma is a chronic disease that affects the lining of the bronchioles, which are the airways in the lungs. The lining of the airways becomes inflamed and swollen and produces extra mucus. Episodes of asthma (called attacks) occur when the airway narrows, making it difficult to breathe.

During an asthma attack, symptoms may range from mild wheezing (whistling or hissing sound when breathing) to severe obstruction of the airways, potentially causing a life-threatening inability to breathe. Although asthma can be very serious, there are many ways to prevent and control symptoms.

The underlying cause of asthma is not known. However, factors in the environment (both indoors and outdoors), called triggers, can make asthma symptoms worse and actually cause an asthma attack.